JPH0341890B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thin film magnetic head used for recording and reproducing digital signals.

Conventional structure and its problems As shown in Figure 1, the conventional magnetoresistive head used for reproducing digital signals, etc., has a ferromagnetic thin film formed in a strip shape perpendicular to the recording medium 1 (in the Y direction). magnetoresistive elements (hereinafter referred to as MR elements) are brought into contact with or in close proximity, electrodes 3 and 4 are placed at both ends of the MR element 2 in the longitudinal direction (Z direction), and a constant current i is applied between the electrodes 3 and 4. The change in the resistance value in the X direction is detected by the voltage change between the electrodes 3 and 4 by applying a signal magnetic field of the recording medium 1 in the Y direction.

Generally, a magnetoresistive head for reproducing is used in close proximity to an inductive thin film magnetic head for recording, either by being built into the same deck or by vapor deposition on the same substrate. At this time, the recording current leaks into the reproduction output (feed-through), making it impossible to reproduce the data signal with simultaneous monitoring that simultaneously reproduces the recorded signals. Furthermore, in order to reduce feed-through or to reproduce short wavelengths, shielded heads have a magnetic air gap on both sides of the MR element, and when bias is applied using an external magnet, the MR element is shielded, so the MR element is shielded. A large external magnetic field is required to provide a strong magnetic field, and as a result, the signal recorded on the medium is demagnetized, and the feed-through is insufficient, making simultaneous monitoring during recording difficult and impractical. As a countermeasure against such feed-through, the following signal processing is available in order to record and reproduce the same data by distributing it to a plurality of tracks. That is,
The same data is recorded on an even number of tracks so that the even numbered track and the odd numbered track are in reverse phase, and during playback, the sum signal of the output from the even numbered track and the output from the odd numbered track are combined. This is a method of canceling out the influence of in-phase feedthrough or noise superimposed on the head wiring by obtaining a subtracted output from the sum signal. In this method, in order to record and reproduce the same signal on a plurality of tracks, it is necessary to have multiple (at least twice) as many recording heads and reproduction heads as the number of signals. There is a problem in that the number of wiring lines increases.

In order to overcome such problems, there is a method of realizing the structure of the reproducing head by the shunt bias method, instead of using a plurality of tracks for recording one data as described above. The shunt bias method, which is a structure of the current bias method, is a shield type that is applied for short wavelength reproduction.
Shown in Figures a and b. It has three terminals 21, 22, 23 including a common ground terminal 21, and the MR element 24 is short-circuited by a resistance element 25 such as T _i , and the MR element 24 is biased by the current flowing through this resistance element 25. Apply a magnetic field. A constant current i is applied to the other two terminals of the MR element 24 from constant current source circuits 26 and 27 so as to flow into the common ground terminal 21, and a bias magnetic field H _B in the opposite direction is applied to the MR element 24. Added from outside. M is MR element 2
4 magnetization direction. kept in this condition
When a signal magnetic field is input to the MR element 24, the signal magnetic field is transmitted to the MR element with the common ground terminal 21 in between.
The two parts of the element 24 are magnetized with opposite phases because the current directions are opposite. When taking the difference signal between the voltages output to the two electrodes, in the shunt bias method the output is generally underbiased, but even if one output is underbiased and the reproduced output is distorted, it will not be distorted mutually with the other output. Since the components are canceled and compensated, the playback output is good, and external noise is also canceled, but azimuth matching is a problem in terms of element uniformity, recording signal uniformity, and compatibility between devices compared to heads with other structures. When I do, I am strictly required to do so.
Not practical. Furthermore, since current is passed through both the MR element and the resistance element, there is a drawback that thermal noise, which is unique to MR elements, increases.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and provides a thin film magnetic head that allows easy azimuth adjustment and does not generate thermal noise.

Structure of the Invention The present invention provides an MR element with three terminals, one of which is used as a reference electrode, this common terminal is grounded in an alternating current manner, one of the other two terminals is grounded via a resistor, and the other is grounded via a resistor. A constant current is supplied from the terminals of the head to obtain a reproduction output of opposite phase, and this is differentially amplified to eliminate the influence of external noise that enters the head and the wiring from the head. By assuming that it is due to anisotropy,
This eliminates mutual interference between the medium and the thin-film head, that is, demagnetization of the medium, and thermal noise peculiar to MR heads, thereby providing a good head without deterioration of the signal-to-noise ratio.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The structure of the MR head of the present invention is as follows:
This is the MR element shown in Figure 1 with three terminals. The MR element 6 is provided with three terminals 7, 8, and 9 for supplying MR current and taking out reproduction output, and terminal 9 of these terminals is grounded via a capacitor 15, that is, AC grounding is performed. If there are a large number of MR elements 6, the number of terminals for wiring can be reduced by making this terminal 9 common and taking it out as a common terminal and connecting it to AC grounding. Terminal 8 is grounded via resistor 13. The resistance value of this resistor 13 is connected to the terminal 7. The value is set to be the same as the equivalent output impedance of the constant current source circuit 12. From the constant current source circuit 12, it flows from terminal 7 to terminal 8 and through resistor 13 to the ground side.
MR currents 10 and 11 are supplied. Since terminal 9 is only connected to AC ground, MR current 10, 11
are exactly the same. Then, a bias magnetic field in the same direction is applied to the MR element 6 from the outside. When the magnetization direction M of the MR element 6 changes due to the signal magnetic field from the magnetic recording medium and its resistance value changes, the MR current is a constant current, so if the resistance value of the MR element 6 becomes small, the terminals 7 and 9 Although the potential between terminals 8 and 8
is a constant potential. The amount of variation in the potential at terminal 7 is twice that at terminal 9.

This results in a varying voltage between terminal 7 and terminal 9, i.e. the reproduction output appearing at terminal 7 and the terminal 8.
The fluctuating voltage applied to terminal 9, that is, the reproduced output appearing at terminal 9, are in opposite phase to each other. terminal 7,
The output appearing at 8 is supplied to the positive and negative inputs of a differential amplifier 14 via capacitors, and differential amplification is performed to obtain a reproduced output from the MR element 6.
Note that the same applies even if the direction of the MR current is opposite to that described above.

By the way, since external noise such as feed-through of recording current is alternating current, it is mixed into the head and the wiring from the head so that it flows toward the alternating current grounding side (lower impedance side). That is, the external noise that enters the MR element and the wiring on the terminal 7 side is in the same phase as the external noise that enters the MR element and the wiring on the terminal 8 side. The minute signal equivalent circuit in the configuration shown in FIG. 3 is as shown in FIG. 4 as described above. There is a signal 16 on the terminal 7 side of the MR element 6, which generates a signal e _s . External noise 18
Represented as e _o . The constant current source is represented by a resistor 20 whose internal impedance has the same value as the resistor 13. On the other hand, there is a signal source 17 on the terminal 8 side of the MR element 6, which generates a signal -e _s that is in phase opposite to the signal e _s on the terminal 7 side, and external noise 19 is expressed as e _o that is in phase with the terminal 8 side. . Since the impedances of the terminal 7 side system and the terminal 8 side system are the same, the external noise has the same e _o on both the terminal 7 side and the terminal 8 side as described above.

As a result of the above, by inputting the signals from the two terminals to the differential amplifier 14, the noise component is canceled in the output, and the signal component is obtained as 2e _s , which is completely unaffected by external noise. No playback output can be obtained. Since the phase of the left and right elements is in the same phase with respect to the terminal 9 where the resistance change of the MR element 6 is common, the fluctuation of the output waveform with respect to the azimuth that appears in the head using the shunt bias method in FIG. 2 can be avoided in the present invention. is not a problem. Furthermore, since no extra current is applied to the tip of the element for the bias means, thermal noise due to Joule heat is reduced. Furthermore, in the present invention,
Since only one constant current source is required, there is an advantage that the circuit configuration is simple.

In order to carry out the present invention more effectively, another embodiment is shown in FIG. 5 in which there is no demagnetization of the medium or generation of noise, that is, no deterioration of the signal S to noise N ratio. This FIG. 5 is a side view of the MR element 6, and the difference from the embodiment shown in FIG. 3 is that when the bias magnetic field of the MR element 6 is as shown in FIG. In contrast, in the case of FIG. 5, the magnetization is directed in the optimum bias direction by induced magnetic anisotropy. This induced magnetic anisotropy is obtained as follows. That is, when the surface of the substrate on which the MR element 6 is deposited is polished in one direction with a wrapping tape or the like, the roughness of the substrate surface follows the lapping streaks and becomes rough anisotropically in a certain direction.
Although the intervals between the wrap marks are random, magnetic domains are generated along the wrap marks, and these magnetic domains are subdivided and have good orientation, resulting in large induced magnetic anisotropy.

Due to the induced magnetic anisotropy imparted as described above, there is no need to apply a bias magnetic field to the MR element 6 by external means, there is no demagnetization of the medium, and there is no heat generation due to the bias current. It is possible to provide the MR element 6 with a head free of thermal noise.

Effects of the Invention As described above, the present invention has been able to provide a thin film magnetic head that has a simple configuration, allows easy azimuth adjustment, and does not generate thermal noise, and has great effects.

[Brief explanation of the drawing]

Figures 1 and 2 a and b are diagrams showing conventional examples, and Figure 3
The figure shows an embodiment of the present invention together with a circuit, FIG. 4 is an equivalent circuit diagram, and FIG. 5 is a side view of a magnetoresistive element of another embodiment. 6... Magnetoresistive element, 7, 8, 9... Terminal, 10, 11... Current, 12... Constant current source circuit, 13... Resistor, 14... Differential amplifier, 15...
...capacitor.

Claims (1)

[Claims] 1. A thin film magnetic head having a magnetoresistive element made of a ferromagnetic material deposited on a substrate,
The magnetization of the magnetoresistive element is biased in a certain direction, a signal magnetic field is applied to this element, the common terminal at the center of the magnetoresistive element is grounded in an alternating current manner, and one of the other two terminals is grounded. The terminal is grounded through a resistor, and by supplying a constant current from the other terminal, the change in resistance value between the common terminal and the other two terminals is differentially extracted as a reproduction voltage. A thin film magnetic head characterized by: